Way to add leading zeroes to binary string in JavaScript [duplicate]

Question

I've used .toString(2) to convert an integer to a binary, but it returns a binary only as long as it needs to be (i.e. first bit is a 1).

So where:

num = 2;
num.toString(2) // yields 10. 

How do I yield the octet 00000010?

Answer 1

It's as simple as

var n = num.toString(2);
n = "00000000".substr(n.length) + n;

Answer 2

You could just use a while loop to add zeroes on the front of the result until it is the correct length.

var num = 2,
    binaryStr = num.toString(2);

while(binaryStr.length < 8) {
    binaryStr = "0" + binaryStr;
}